Lord Birt, the former BBC director general and producer of the late Sir David Frost's celebrated interview with Richard Nixon, has told how the veteran broadcaster ended "the age of deference" and ushered in a new era that made programmes like Newsnight and the Today programme possible.

Birt, speaking on BBC Radio 4's Today programme on Monday following Frost's death at the weekend, spoke of the lengths he went to get the Nixon interview and how after months of preparation they thought they would never extract the famous Watergate confession in which the disgraced president told the American people he had let them and the country down.

After two months of interviews in which Nixon persisted with his line that he had done nothing wrong, he cracked, Birt recalled. "It was like being at a birth," Birt told Today. "He said it because in the end David had him on the ropes so many times before you heard those words, he completely out-argued him."

Reflecting on his contribution to broadcasting, Birt described Frost as "a critical part of the 60s". He said the satirical show he helped found, That Was The Week That Was, was "a cultural bombshell" and its impact was "very hard for people to imagine now".

Frost's second legacy, Birt said, was he inventing the modern interview. "He ushered in the end of the age of deference and made honourable programmes like [Today] and Newsnight possible."

Birt recalled how Frost only got the interview with Nixon because he raised the money personally, outbidding a US broadcaster.

"He got the interview because he bid more than anyone. Only one of the American networks wanted it. He outbid the American network. He didn't have the money at that point, he only told me very recently that he had to sell his LWT shares which if he had held on to them would have been worth tens of millions of pounds," said Birt.

Then when he clinched the deal he had another struggle on his hands – none of the networks wanted to air the interviews. "He thought they would jump at the chance, they didn't. He had to create a net and sell the ads himself, so while we were preparing these historic interviews, David was very very worried about making it work as a financial proposition," said Birt.

Having clinched the exclusive deal for four interviews, Birt and Frost spent two months interviewing Nixon, conducting three two-hour sessions a week. The Watergate apology came during the second session on the scandal, which had linked Nixon to a burglary of the Democratic National Committee headquarters in a Washington complex known as Watergate in 1972.

Birt recalled how Nixon was well prepared on other subjects such as Vietnam and China, but how he later learned he had done no preparation on Watergate.

"Nixon did not come prepared to say those words. That was the culmination of nearly four hours of interview," he said. "Why did he say it? he said it because in the end David had him on the ropes so many times before you heard those words, he completely out-argued him ... It was like being at a birth to be honest ... In a sense it was the final denouement. America waited three years for its president. it was the end of Watergate episode. America then turned the page – what he said was considered enough."

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